How to make it 30 minutes, plus chilling

Meanwhile, in a saucepan, sprinkle unflavored gelatin over 1/2 cup cold water; let stand for 1 minute. Add the cream and sugar; cook and stir over low heat until gelatin and sugar are completely dissolved. cool to room temperature. Whisk in sour cream and vanilla. Spoon over the blue layer. Refrigerate until firm.